How does high porosity increase the water retaining capacity?
Answers
Answer:
Yes, for soils surrounded by impervious strata, both below and around.
Water is held by soils by soaking of particles and capillary action. Water has to permeate into the strata for doing this (the strata not being very thin), which requires some voids. As the voids increase, the particles reduce, easier water flow takes place and capillary action reduces. Faster water flow means less soaking time for the particles. So there is a desirable void ratio, depending on the soil type, for maximum holding capacity.
Explanation:
Soil water holding capacity is controlled primarily by the soil texture and the soil organic matter content. Soil texture is a reflection of the particle size distribution of a soil. An example is a silt loam soil that has 30% sand, 60% silt and 10% clay sized particles. In general, the higher the percentage of silt and clay sized particles, the higher the water holding capacity. The small particles (clay and silt) have a much larger surface area than the larger sand particles. This large surface area allows the soil to hold a greater quantity of water. The amount of organic material in a soil also influences the water holding capacity. As the level of organic matter increases in a soil, the water holding capacity also increases, due to the affinity of organic matter for water.Once water enter a soil profile, one part of it is stored in rooting zone for plant use, some will evaporate and some will drain away from root zone. Plant available water is the difference between field capacity and the wilting point . Beyond the wilting point there is still water in the soil profile, however it is contained in pores that are too small for plant roots to access. Soil texture, soil structure and plant rooting depth are the crucial factors in determining the amount of water available for plants to access.1) Coarser textured soils will generally have larger pore sizes and little soil structure, resulting in rapid water drainage. A poor or non-existent soil structure will have a reduced volume of soil pores. Soil aggregates create pores which store water for plants to access.
(2) Increasing soil organic matter content helps create and stabilise soil structure. Organic matter is considered integral in the capacity of a soil to maximise water storage through its effect on creating and stabilising soil pores and its absorption capacity.